write new draft of typestate advanced intro

this is again in the flow of a problem statement first,
building on our original example,
and in next slide we'll add the solution with generics

Author: GlenDC

src/SUMMARY.md

@@ -439,6 +439,7 @@
     - [Is It Encapsulated?](idiomatic/leveraging-the-type-system/newtype-pattern/is-it-encapsulated.md)
   - [Typestate Pattern](idiomatic/leveraging-the-type-system/typestate-pattern.md)
     - [Typestate Pattern Example](idiomatic/leveraging-the-type-system/typestate-pattern/typestate-example.md)
+    - [Beyond Simple Typestate](idiomatic/leveraging-the-type-system/typestate-pattern/typestate-advanced.md)
     - [Typestate Pattern with Generics](idiomatic/leveraging-the-type-system/typestate-pattern/typestate-generics.md)
 
 ---

src/idiomatic/leveraging-the-type-system/typestate-pattern/typestate-advanced.md

@@ -0,0 +1,96 @@
+## Beyond Simple Typestate
+
+How do we manage increasingly complex configuration flows with many possible
+states and transitions, while still preventing incompatible operations?
+
+```rust
+struct Serializer {/* [...] */}
+struct SerializeStruct {/* [...] */}
+struct SerializeStructProperty {/* [...] */}
+struct SerializeList {/* [...] */}
+
+impl Serializer {
+    // TODO, implement:
+    //
+    // fn serialize_struct(self, name: &str) -> SerializeStruct
+    // fn finish(self) -> String
+}
+
+impl SerializeStruct {
+    // TODO, implement:
+    //
+    // fn serialize_property(mut self, name: &str) -> SerializeStructProperty
+
+    // TODO,
+    // How should we finish this struct? This depends on where it appears:
+    // - At the root level: return `Serializer`
+    // - As a property inside another struct: return `SerializeStruct`
+    // - As a value inside a list: return `SerializeList`
+    //
+    // fn finish(self) -> ???
+}
+
+impl SerializeStructProperty {
+    // TODO, implement:
+    //
+    // fn serialize_string(self, value: &str) -> SerializeStruct
+    // fn serialize_struct(self, name: &str) -> SerializeStruct
+    // fn serialize_list(self) -> SerializeList
+    // fn finish(self) -> SerializeStruct
+}
+
+impl SerializeList {
+    // TODO, implement:
+    //
+    // fn serialize_string(mut self, value: &str) -> Self
+    // fn serialize_struct(mut self, value: &str) -> SerializeStruct
+    // fn serialize_list(mut self) -> SerializeList
+
+    // TODO:
+    // Like `SerializeStruct::finish`, the return type depends on nesting.
+    //
+    // fn finish(mut self) -> ???
+}
+```
+
+<details>
+
+- Building on our previous serializer, we now want to support **nested
+  structures** and **lists**.
+
+- However, this introduces both **duplication** and **structural complexity**.
+
+  `SerializeStructProperty` and `SerializeList` now share similar logic (e.g.
+  adding strings, nested structs, or nested lists).
+
+- Even more critically, we now hit a **type system limitation**: we cannot
+  cleanly express what `finish()` should return without duplicating variants for
+  every nesting context (e.g. root, struct, list).
+
+- To better understand this limitation, let’s map the valid transitions:
+
+```bob
+    +-----------+   +---------+------------+-----+
+    |           |   |         |            |     |
+    V           |   V         |            V     |
+                +                                |
+serializer --> structure --> property --> list +-+
+
+    |             ^           |
+    V             |           |
+                  +-----------+
+  String
+```
+
+- From this diagram, we can observe:
+  - The transitions are recursive
+  - The return types depend on _where_ a substructure or list appears
+  - Each context requires a return path to its parent
+
+- With only concrete types, this becomes unmanageable. Our current approach
+  leads to an explosion of types and manual wiring.
+
+- In the next chapter, we’ll see how **generics** let us model recursive flows
+  with less boilerplate, while still enforcing valid operations at compile time.
+
+</details>

src/idiomatic/leveraging-the-type-system/typestate-pattern/typestate-generics.md

@@ -1,141 +1,13 @@
 ## Typestate Pattern with Generics
 
-Generics can be used with the typestate pattern to reduce duplication and allow
-shared logic across state variants, while still encoding state transitions in
-the type system.
+TODO
 
-```rust
-#[non_exhaustive]
-struct Insecure;
-struct Secure {
-    client_cert: Option<Vec<u8>>,
-}
-
-trait Transport {
-    /* ... */
-}
-impl Transport for Insecure {
-    /* ... */
-}
-impl Transport for Secure {
-    /* ... */
-}
-
-#[non_exhaustive]
-struct WantsTransport;
-struct Ready<T> {
-    transport: T,
-}
-
-struct ConnectionBuilder<T> {
-    host: String,
-    timeout: Option<u64>,
-    stage: T,
-}
-
-struct Connection {/* ... */}
-
-impl Connection {
-    fn new(host: &str) -> ConnectionBuilder<WantsTransport> {
-        ConnectionBuilder {
-            host: host.to_owned(),
-            timeout: None,
-            stage: WantsTransport,
-        }
-    }
-}
-
-impl<T> ConnectionBuilder<T> {
-    fn timeout(mut self, secs: u64) -> Self {
-        self.timeout = Some(secs);
-        self
-    }
-}
-
-impl ConnectionBuilder<WantsTransport> {
-    fn insecure(self) -> ConnectionBuilder<Ready<Insecure>> {
-        ConnectionBuilder {
-            host: self.host,
-            timeout: self.timeout,
-            stage: Ready { transport: Insecure },
-        }
-    }
-
-    fn secure(self) -> ConnectionBuilder<Ready<Secure>> {
-        ConnectionBuilder {
-            host: self.host,
-            timeout: self.timeout,
-            stage: Ready { transport: Secure { client_cert: None } },
-        }
-    }
-}
-
-impl ConnectionBuilder<Ready<Secure>> {
-    fn client_certificate(mut self, raw: Vec<u8>) -> Self {
-        self.stage.transport.client_cert = Some(raw);
-        self
-    }
-}
-
-impl<T: Transport> ConnectionBuilder<Ready<T>> {
-    fn connect(self) -> std::io::Result<Connection> {
-        // ... use valid state to establish the configured connection
-        Ok(Connection {})
-    }
-}
-
-fn main() -> std::io::Result<()> {
-    let _conn = Connection::new("db.local")
-        .secure()
-        .client_certificate(vec![1, 2, 3])
-        .timeout(10)
-        .connect()?;
-    Ok(())
-}
+```rust,editable
+// TODO
 ```
 
 <details>
 
-- This example extends the typestate pattern using **generic parameters** to
-  avoid duplication of common logic.
-
-- We use a generic type `T` to represent the current stage of the builder, and
-  share fields like `host` and `timeout` across all stages.
-
-- The transport phase uses `insecure()` and `secure()` to transition from
-  `WantsTransport` into `Ready<T>`, where `T` is a type that implements the
-  `Transport` trait.
-
-- Only once the connection is in a `Ready<T>` state, we can call `.connect()`,
-  guaranteed at compile time.
-
-- Using generics allows us to avoid writing separate `BuilderForSecure`,
-  `BuilderForInsecure`, etc. structs.
-
-  Shared behavior, like `.timeout(...)`, can be implemented once and reused
-  across all states.
-
-- This same design appears
-  [in real-world libraries like **Rustls**](https://docs.rs/rustls/latest/rustls/struct.ConfigBuilder.html),
-  where the `ConfigBuilder` uses typestate and generics to guide users through a
-  safe, ordered configuration flow.
-
-  It enforces at compile time that users must choose protocol versions, a
-  certificate verifier, and client certificate options, in the correct sequence,
-  before building a config.
-
-- **Downsides** of this approach include:
-  - The documentation of the various builder types can become difficult to
-    follow, since their names are generated by generics and internal structs
-    like `Ready<T>`.
-  - Error messages from the compiler may become more opaque, especially if a
-    trait bound is not satisfied or a state transition is incomplete.
-
-    The error messages might also be hard to follow due to the complexity as a
-    result of the nested generics types.
-
-- Still, in return for this complexity, you get compile-time enforcement of
-  valid configuration, clear builder sequencing, and no possibility of
-  forgetting a required step or misusing the API at runtime.
+- TODO
 
 </details>